Combined check valve and pressure relief valve

ABSTRACT

A combination check valve and pressure relief valve is provided for use in regulating the flow of fluid between a first fluid side and a second fluid side. The valve may include a valve body, a valve insert positioned within an aperture of the valve body, a check poppet attached to the valve insert, and a check spring positioned between the valve insert and the valve body. In addition, a relief spring and a relief poppet may be positioned within a cavity formed by the valve insert and secured in position by the check poppet. The combination of the valve insert and the check poppet is adapted to move relative to the valve body and against the force of the check spring to permit fluid to pass from the first fluid side to the second fluid side, and the relief poppet is adapted to move relative to the check poppet against the force of the relief spring to allow fluid to pass from the second fluid side to the first fluid side.

CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.10/435,365 filed on May 9, 2003 now U.S. Pat. No. 7,028,708. This priorapplication is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

This invention relates generally to the design of valves and moreparticularly, to the design of a combination check valve and pressurerelief valve.

DESCRIPTION OF THE PRIOR ART

Check valves and pressure relief valves are known in the art. Generally,a check valve acts to restrict flow in one direction, while a reliefvalve is used to regulate pressure. U.S. Pat. No. 4,948,092 discloses acombined check valve and pressure relief valve having a resilientduckbill valve body that is manually operated. Fluid passing through acylindrical core around a valve actuator functions to open the lips ofthe duckbill valve body to permit the free flow of the fluid while backpressure functions to seal the lips of the duckbill valve. Manualdepression of the valve actuator, however, causes the valve actuator topenetrate and open the valve lips to selectively permit backflow toprovide the relief valve function. It is also known to provide checkvalve and pressure relief functions that are activated by the pressureof the hydraulic fluid.

Although these valves are capable of achieving their intended purpose,valves actuated by fluid pressure must be set during assembly to thedesired activation pressure or flow rate. For example, in some prior artvalves, this procedure is performed by subjecting the valve to pressureand then manually adjusting the setting. In other prior art valves, thevalve is adjusted by measuring a compression force on the valve springand then locking the valve insert once the desired activation pressureor flow is established. These setting procedures are time consuming andadd to the cost of installation for valves.

SUMMARY OF THE INVENTION

To overcome these, and other disadvantages, a combination check valveand pressure relief valve is provided for use in regulating the flow offluid between a first fluid side and a second fluid side. The valve mayinclude a valve body, a valve insert positioned within an aperture ofthe valve body, a check poppet attached to the valve insert, and a checkspring positioned between the valve insert and the valve body. Inaddition, a relief spring and a relief poppet may be positioned within acavity formed by the valve insert and secured in position by the checkpoppet. The combination of the valve insert and the check poppet isadapted to move relative to the valve body and against the force of thecheck spring to permit fluid to pass from the first fluid side to thesecond fluid side, and the relief poppet is adapted to move relative tothe check poppet against the force of the relief spring to allow fluidto pass from the second fluid side to the first fluid side.

A better understanding of these and other advantages, objects, features,properties and relationships of the invention will be obtained from thefollowing detailed description and accompanying drawings, which setforth illustrative embodiments and which are indicative of the variousways in which the principles of the invention may be employed. Otherbenefits and objects of this invention are disclosed herein and will beobvious to readers of ordinary skill in the art. It should beappreciated by those with skill in the art, however, that the disclosedembodiments may be used in a wide variety of applications where both acheck valve and relief valve function is required.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, reference may be had to thefollowing drawings in which:

FIG. 1 depicts a rear elevational view of a vehicle including atransaxle incorporating the present invention;

FIG. 2 depicts a cross-sectional, front view of the transmission shownin FIG. 1;

FIG. 3 depicts a side view of the transaxle shown in FIG. 1 with certainportions, including the side housing, removed for clarity;

FIG. 4 depicts a side view of a first embodiment of a combination checkvalve and pressure relief valve;

FIG. 5 depicts a perspective view of the valve shown in FIG. 4;

FIG. 6 depicts an exploded perspective view of the valve shown in FIG.4;

FIG. 7 depicts a sectional view of the valve shown in FIG. 4 along linesA-A with the check poppet and relief poppet portions in the closedposition;

FIG. 8 depicts an orthogonal, sectional view of the valve shown in FIG.7;

FIG. 9 depicts a sectional view of the valve shown in FIG. 4 with thecheck poppet in the open position;

FIG. 10 depicts a sectional view of the valve shown in FIG. 4 with therelief poppet portion in the open position;

FIG. 11 depicts a sectional view of a center section for a single pumphydrostatic transmission in which the valve shown in FIGS. 4 through 10is installed;

FIG. 12 depicts a perspective view of a first embodiment of a reliefpoppet;

FIG. 13 depicts a side view of the relief poppet shown in FIG. 12;

FIG. 14 is a graph illustrating the performance characteristic of avalve incorporating the first embodiment of the relief poppet shown inFIG. 12;

FIG. 15 depicts a perspective view of a second embodiment of a reliefpoppet;

FIG. 16 depicts a side view of the relief poppet shown in FIG. 15;

FIG. 17 is a graph illustrating the performance characteristic of avalve incorporating the second embodiment of the relief poppet shown inFIG. 15;

FIG. 18 depicts a perspective view of a third embodiment of a reliefpoppet;

FIG. 19 depicts a side view of the relief poppet shown in FIG. 18;

FIG. 20 is a graph illustrating the performance characteristic of avalve incorporating the third embodiment of the relief poppet shown inFIG. 18;

FIG. 21 depicts a side view of a second embodiment of a combinationcheck valve and pressure relief valve;

FIG. 22 depicts a sectional view of the valve shown in FIG. 21 along thelines B-B;

FIG. 23 depicts a perspective view of the valve shown in FIG. 21;

FIG. 24 depicts a side view of a third embodiment of a combination checkvalve and relief valve;

FIG. 25 depicts a sectional view of the valve shown in FIG. 24 along thelines C-C;

FIG. 26 is a perspective view of the valve shown in FIG. 24.

FIG. 27 depicts a sectional view of the valve shown in FIG. 24 with theinternal springs removed;

FIG. 28 depicts a side view of a fourth embodiment of a combinationcheck valve and relief valve;

FIG. 29 depicts a sectional view of the valve shown in FIG. 28 along thelines D-D;

FIG. 30 depicts a perspective view of the valve shown in FIG. 28;

FIG. 31 depicts a sectional of the valve shown in FIG. 28 with theinternal springs removed;

FIG. 32 depicts a side view of a fifth embodiment of a combination checkvalve and relief valve.

FIG. 33 depicts a sectional view of the valve shown in FIG. 32 along thelines E-E;

FIG. 34 depicts a perspective view of the valve shown in FIG. 32.

DETAILED DESCRIPTION

Turning now to the figures, wherein like reference numerals refer tolike elements, there is generally illustrated in FIGS. 4 to 11 acombination check valve and pressure relief valve (“valve”) 30. Inaddition, throughout the following description several embodiments ofthe valve 30 or other elements may be described. Any reference toelements that are described in more than one embodiment will be giventhe same number that the element was given in the first embodiment withan additional prefix numeral, except for the first embodiment which willnot receive a prefix numeral. While valve 30 will be described in thecontext of a hydrostatic transmission, it should be understood by thoseof ordinary skill that valve 30 may also be utilized in connection witha myriad of additional applications. In addition, the valve 30 shownherein may be easily assembled into a cartridge configuration andrequires no special tools or procedures to adjust/set the pressurerelief setting.

FIG. 1 shows a typical vehicle 10 in which a hydrostatic transaxle 12 ismounted. FIG. 2 shows a cross-sectional view of the hydraulic componentsof transaxle 12. Generally, such devices operate on the principal of aninput shaft 14 driving a hydraulic pump 16. As pump 16 rotates itdisplaces fluid through porting 23 located in a center section 22 todrive a motor 20, all of which are located within a generally fluidfilled sump 26. As shown in FIG. 3, motor 20 is also associated with ashaft 24 that is capable of driving a gear train 25, which may furtherdrive wheels 11 of a vehicle 10. Although this description describes ahydrostatic transaxle containing an axial piston pump and axial pistonmotor, it should be appreciated that the disclosed embodiments may alsobe used in conjunction with a variety of hydraulic devices such asstand-alone hydraulic pumps or motors that may be of otherconfigurations, such as radial piston, gerotor, and the like. For a moredetailed description of the principles of operation of a hydrostatictransmission, the reader is referred to U.S. Pat. Nos. 5,201,692, and6,322,474, which are incorporated herein by reference in their entirety.

As noted above and as shown in FIG. 11, for placing hydraulic pump 16 influid communication with hydraulic motor 20, center section 22 includeshydraulic porting 23. Hydraulic porting 23 is in further fluidcommunication with a source of makeup fluid, such as a fluid sump 26 ora charge gallery. Generally, the hydraulic porting comprises a highpressure side through which fluid moves from hydraulic pump 16 tohydraulic motor 20 and a low pressure side through which fluid returnsfrom hydraulic motor 20 to hydraulic pump 16. Since fluid tends to leakfrom various components, hydraulic pump 16 generally requires more fluidthan is returned from hydraulic motor 20 via the low pressure sideporting. This requirement for fluid may be satisfied by using valve 30.Generally, valve 30 functions to prevent the flow of fluid fromhydraulic porting 23 to the source of makeup fluid, while also allowingfluid to flow from the source of makeup fluid into hydraulic porting 23when the fluid pressure in the hydraulic porting is lower relative tothe fluid pressure in the source of makeup fluid. In cases where thefluid pressure in hydraulic porting 23 is excessive, determined on anapplication by application basis, valve 30 further functions to relievethis excess fluid pressure by allowing fluid to be discharged fromhydraulic porting 23 to the source of makeup fluid.

To this end, valve 30 may be mounted in center section 22 between afirst fluid side A and second fluid side B. In the application describedherein, the first fluid side A is associated with the source of makeupfluid while the second fluid side B is associated with the porting thatprovides a fluid path between hydraulic pump 16 and hydraulic motor 20.By way of example, FIG. 11 illustrates valve 30 installed in anexemplary center section 22 for a hydrostatic transmission carried aspart of an integrated hydrostatic transaxle. It should be appreciated bythose with skill in the art, however, that the illustrated embodimentsis not intended to be limiting and that valve 30 may be used inconnection with other applications.

The preferred embodiment of the present invention utilizes screw threadsto attach valve 30 to center section 22. Other means for securing valve30 to center section 22 are known in the art.

To allow for the flow of fluid from fluid side A to fluid side B whenfluid side B is under lower pressure relative to fluid side A, valve 30is comprised of a valve body 32 having an aperture 33, a valve insert 36that is slidably positioned within aperture 33 and a check poppet 42.More specifically, valve insert 36 has a first end 36A and a second end36B, the first end 36A of valve insert 36 being positioned within andextending through aperture 33 and the second end 36B of valve insertforming a valve stop 37. Check poppet 42 is attached to the first end36A of valve insert 36 and the combination of valve insert 36 and checkpoppet 42 form a unitary valve 30, while maintaining the slidablerelationship with valve body 32. The valve stop 37 may form variousshapes and sizes, however, the length of the valve stop 37, which shallbe defined as the greatest horizontal dimension of the valve stop 37,must exceed the diameter of the aperture 33. It should also beunderstood that the valve stop 37 may exist as an integral portion ofvalve insert 36 or as a separate and distinct portion capable of beingremovably attached to valve insert 36.

For creating a biasing relationship between valve body 32 and thecombination of valve insert 36 and check poppet 42, valve 30 may includea check spring 34 as illustrated in FIGS. 4 to 11. Check spring 34 isoptional in the embodiments described herein, but in some situations,such as inverted orientation, check spring 34 may improve the operatingcharacteristics of a transaxle. Furthermore, as will be obvious to oneskilled in the art, fluid flow through the valve is simplified andimproved when check spring 34 is removed; in this situation thealternative fluid paths through valve insert 36 from sump 26 to porting23 described below are unnecessary and may be eliminated.

Optional check spring 34 is positioned between valve insert 36 and valvebody 32. More specifically, check spring 34 is placed within aperture 33of valve body 32 and rests against lip 35, which is formed on aninternal portion of valve body 32. The other end of check spring 34rests on valve stop 37.

For connecting first end 36 A of valve insert 36 to check poppet 42, thefirst end 36A of valve insert 36 extends through aperture 33 of valvebody 32 and includes screw threads 44. As shown in FIGS. 7 to 11, thescrew threads are capable of removably connecting valve insert 36 tocheck poppet 42. The combination of valve insert 36 and check poppet 42allows the slidable relationship with valve body 32 to be assumed.Although the preferred embodiment of the present invention includes athreaded relationship between valve insert 36 and check poppet 42, itshould be understood that other means for removably connecting valveinsert 36 to check poppet 42 may also be used, such as retaining rings,a snap fit, etc.

When the force on check poppet 42, caused by the fluid pressure fromfluid side A being greater than the fluid pressure on fluid side B (the“check pressure differential”), is sufficient to overcome the restoringforce of the check spring 34, the check pressure differential willinfluence the movement of check poppet 42 away from valve body 32 untilvalve stop 37 contacts step 48 of valve body 32, thereby compressingcheck spring 34 into valve body 32. As shown in FIG. 9, this movementcreates a gap 51 between valve body 32 and check poppet 42. In thismanner, the movement of check poppet 42 away from valve body 32 breaks asealing engagement between check poppet 42 and valve body 32, therebyallowing the fluid under pressure in fluid side A to flow into fluidside B. As shown in FIG. 9, hydraulic fluid flows from sump 26 (notshown), through the space between valve insert 36 and valve body 32where spring 34 is located, and then through gap 51 into porting 23 (notshown). Hydraulic fluid may optionally flow through openings 47 and intothe central hollow portion of valve insert 36. The hydraulic fluid maythen flow out through openings 49 and into gap 51. Fluid should be ableto flow readily through either the space between valve body 32 and valveinsert 36 or through the route formed in valve insert 36 by opening 47and opening 49, or through both routes, to provide a minimal pressuredrop for fluid entering porting 23 under the anticipated environmentaland performance conditions for valve 30 to function properly.

Once the check pressure differential and flow of fluid from fluid side Ais no longer sufficient to overcome the restoring force of check spring34, the return force provided by check spring 34 urges valve insert 36away from valve body 32, which directs check poppet 42 back towardsvalve body 32. As shown in FIGS. 7 and 8, movement of check poppet 42back towards valve body 32 functions to return check poppet 42 intosealing engagement with valve body 32, thereby preventing the flow offluid between porting 23 and sump 26 through gap 51. In a valveconfiguration where the opening of the valve is oriented downwards, ortowards the ground, the force of gravity is usually sufficient to movecheck poppet 42 toward valve body 32. In other orientations, buildingsystem pressure will also force check poppet 42 toward valve body 32;however, use of optional check spring 34 may provide improved smoothnessof transition from when the check poppet 42 is in the unseated or openposition to the seated or closed position, thus, minimizing a possiblejerk as system pressure builds rapidly once the check poppet is restoredto the seated position.

To allow for the flow of fluid from fluid side B to fluid side A whenthe fluid in fluid side B is at a predetermined pressure relative to thefluid in fluid side A, relief poppet 40 may be moved from a sealedposition (as shown in FIGS. 7 and 8) to an open position (as shown inFIG. 10). When relief poppet 40 is in the open position, fluid will flowfrom porting 23 through opening 43 of check poppet 42, around theperiphery of relief poppet 40 and through the central portion of valveinsert 36. Then, fluid will flow out of passage 49 past valve insert 36and into sump 26, or out passage 47 past the open areas of valve stop 37into sump 26. Therefore, when the fluid pressure from fluid side B isgreater than the force on fluid side A (the “relief pressuredifferential”) and the force resulting from the relief pressuredifferential is sufficient to overcome the restoring force of reliefspring 38, fluid may flow from fluid side B to fluid side A. At leastone of the passages 47, 49 or an equivalent is required for the reliefvalve function to be effective.

When the relief pressure differential is no longer sufficient toovercome the restoring force of relief spring 38, relief spring 38forces the relief poppet 40 back towards opening 43 in check poppet 42.As shown in FIGS. 7 and 8, movement of relief poppet 40 back towardscheck poppet 42 functions to return relief poppet 40 into sealingengagement with check poppet 42 to thereby restrict the flow of fluidfrom porting 23 around relief poppet 40 to sump 26.

For establishing the pressure relief setting for the valve 30, checkpoppet 42 is tightened on screw threads 44 until a torque level isachieved that indicates valve insert 36 has contacted inside surface 46of check poppet 42, thereby compressing relief spring 38 andestablishing the pressure at which the relief portion of valve 30 willopen. Further, when check poppet 42 is secured to valve insert 36, allcomponents of valve 30 are secured such that valve 30 becomes a completeassembly with a pre-established pressure relief setting.

Since the relief pressure is set by the physical configuration of valve30 components, no steps are required to set the check or relief springs34, 38 to a particular spring compression during assembly orinstallation of valve 30. Therefore, cost of assembly for the describedvalve 30 is also reduced. Rather, the desired fluid flow at a desiredopening pressure is a function of the spring constants, physicaldimensions, and amount of compression of check spring 34 and reliefspring 38, which may be calculated in a manner well known to those ofskill in the art.

To reduce the aggressiveness of the efficient hydraulics during vehicleacceleration and deceleration, an optional bleed passage 41 isincorporated into relief poppet 40. The bleed passage 41 provides a flowpath for the hydraulic fluid from porting 23 through valve insert 36 andto sump 26. For providing a fluid seal when relief poppet 40 is in aclosed position, the preferred embodiment of the present inventionincludes a relief poppet 40 with a substantially spherical surface 45.While the spherical surface is preferred for engaging the periphery ofpassage 43, it should be understood that many other shapes for reliefpoppet 40 may be employed to accomplish similar functionality. Reliefpoppet 40 may also include a spherical surface on each side so thatrelief poppet 40 may be properly installed regardless of which sidecooperates with opening 43. It should be appreciated, however, that bothsides of the relief poppet 40 are not required to be the same shape.

For sealing valve 30 against raised boss 54, which extends from centersection 22 through a hole 56 located in filter wall 58 of filter 60 (asshown in FIG. 11), valve 30 may include a washer 50 and o-ring 52.Washer 50 aids in properly locating valve 30 and properly compressingo-ring 52 for sealing. Details of the configuration assumed by washer 50and o-ring 52 shown in FIG. 6 are disclosed in U.S. Pat. No. 6,122,996,incorporated by reference herein in its entirety. It should beemphasized that while washer 50 functions to assist in the retention offilter 60, it is not a required element of the valve. Furthermore,o-ring 52 may also be eliminated in certain operational circumstanceswhere the sealing and pre-load benefits of o-ring 52 are not desired orrequired.

As shown in FIG. 11, valve 30 may also be associated with additionalcomponents, such as a bypass mechanism. While it is commonly known inthe art to provide a bypass mechanism, such as that shown in U.S. Pat.No. 6,122,996 referenced above, in order for the bypass mechanism to beeffective, check poppet 42 or similar element of valve 30 must bemoveable, thereby allowing fluid to flow between fluid side A and fluidside B when the bypass is actuated. To actuate the bypass mechanism inthe preferred embodiment of valve 30, a portion of valve insert 36 isconfigured to allow bypass actuator 62 to contact it and move it whenbypass rod 64 is actuated. When bypass rod 64 is actuated, it contactsvalve stop 37, thereby causing valve insert 36 to slide within valvebody 32, thereby lifting check poppet 42 from its sealing engagementwith valve body 32, which will allow fluid to flow between porting 23and sump 26.

As mentioned above, it should be understood by those with skill in theart that many different relief poppet 40 designs may be employed. Itshould also be understood that the performance of valve 30 may vary as aresult of the relief poppet 40 design that is incorporated, asexemplified by the following embodiments of relief poppet 40 and thecorresponding performance curves described below.

A first embodiment relief poppet 40 is shown in FIGS. 12 and 13. Thisembodiment is called a “squaucer” because of the combination of agenerally square outer periphery and spherical, flying saucer-like,upper and lower surfaces. An approximate performance curve for thisembodiment is provided in FIG. 14.

A second embodiment relief poppet 140 is shown in FIGS. 15 and 16. Thisembodiment has replaced the spherical surface of the previous embodimentthat interfaces with relief spring 38 with a slot 66 and cutout portions67. This configuration is shown without an optional bleed passage, andhas the approximate performance characteristic shown in FIG. 17.

A third embodiment relief poppet 240 is shown in FIGS. 18 and 19. Thisembodiment has a generally circular outer periphery and has an overallshape described as “flying saucer.” The approximate performance curvefor this embodiment is provided in FIG. 20.

A second embodiment of the valve, i.e., valve 130, is shown in FIGS. 21,22, and 23. Check poppet 142 extends through valve body 132, and valveinsert 136 is attached to check poppet 142 by means of threads formed oncheck poppet 142 to retain the internal elements of valve 130. Ball 68serves in place of relief poppet 40. Passage 147 is provided in valveinsert 136 to allow pressure relieved fluid to escape to sump 26. Valveinsert 136 also includes valve stops 137, which are spaced about theperiphery of valve insert 136, to limit the movement of the centralportion of valve 130. In addition, similar to the fluid flow created inthe first embodiment of the valve, when conditions cause valve 130 tooperate as a check valve, gaps adjacent to valve stops 137 provide spacethrough which fluid may enter valve 130 and porting 23.

A third embodiment of the valve, i.e., valve 230, is shown in FIGS. 24to 27. Check poppet 242 in this embodiment comprises legs 70, each ofwhich have a locking feature 72 used to capture valve insert 236. Thespace between legs 70 and passage 247 allows fluid to freely flow to orfrom porting 23 depending on whether check poppet 242 or relief poppet40 opens, respectively. Valve insert 236 also includes valve stops 237,which are spaced about the periphery of valve insert 236, to limit themovement of the central portion of valve 230.

A fourth embodiment of the valve, i.e., valve 330, is shown in FIGS. 28through 31. Pin 74 inserted through a pair of holes 76A, 76B, or 76C actto constrain the internal components of valve 330. In this embodiment,each pair of holes 76A, 76B, or 76C are located at varying distancesfrom the top portion of the check poppet 342. To vary the amount ofcompression that relief spring 338 exerts, therefore, pin 74 may beinserted into holes which are closer or farther from the top portion ofcheck poppet 342. The placement of pin 74 with respect to the topportion of check poppet 342 may also cause the gap between check poppet342 and valve body 332 to vary, which would affect fluid flow betweensump 26 and porting 23. It should also be understood that pin 74 may beused as a valve stop in this embodiment and others.

A fifth embodiment of the valve, i.e., valve 430, is shown in FIGS. 32through 34. Check poppet 442 has legs 470, which extend past valveinsert 436 and which cooperate with retaining ring 78. For retainingvalve insert 436 and the other internal components of valve 430, valveinsert 436 is positioned between an undercut formed in check poppet 442and retaining ring 78. Further, retaining ring 78 is positioned betweenvalve insert 436 and legs 470, and legs 470 are removably attached toretaining ring 78. Therefore, valve insert 436 is locked between checkpoppet 442 and retaining ring 78. Retaining ring 78 is located within anundercut formed in legs 470 of check poppet 442. The portion of valveinsert 426 that extends outside of retaining ring 78 acts as a valvestop 437.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. For example, whilevalve 30 is illustrated as being positioned in one side of a hydrauliccircuit, it will be appreciate that such a valve 30 can also bepositioned in the opposite side of a hydraulic circuit. Further, it maybe desirable to include such valves on both sides of a hydrauliccircuit. In addition, it should be appreciated by those with skill inthe art that each of the different embodiments of the valve describedherein may include valve inserts having one or more valve stops and thatthe valve stops may form integral or separate portions of the respectivevalve insert. Moreover, each of the various valve stop designs discussedabove may be used in connection with different valve designs as desired.Accordingly, the particular arrangement disclosed is meant to beillustrative only and not limiting as to the scope of the inventionwhich is to be given the full breadth of the appended claims and anyequivalents thereof.

1. A valve for use in regulating the flow of fluid between a first fluidside and a second fluid side in a hydraulic circuit, comprising: a valvebody comprising: a first end; a second end; and an aperture extendingfrom the first end to the second end, the aperture having a firstdiameter; a valve insert having a second diameter, which is less thanthe first diameter, the valve insert extending into the aperture, thevalve insert having a valve stop with a length greater than the firstdiameter of the aperture, the valve stop positioned proximate to thefirst end of the valve body wherein a fluid flow space is createdbetween the first diameter and the second diameter; and a check poppet,at least a portion of which has a third diameter greater than the firstdiameter, the check poppet attached to the valve insert proximate to thesecond end of the valve body; wherein fluid passes through the fluidflow space as it flows from the first fluid side to the second fluidside of the hydraulic circuit.
 2. The valve as set forth in claim 1,wherein the valve insert comprises an internal volume.
 3. The valve asset forth in claim 2, further comprising a relief spring and a reliefpoppet positioned in the internal volume, wherein the relief springbiases the relief poppet to engage an opening formed in the checkpoppet.
 4. The valve as set forth in claim 3, wherein the relief poppetmoves away from the check poppet opening when the fluid pressure in thefirst fluid side exceeds the pressure in the second fluid side by apre-determined amount.
 5. The valve as set forth in claim 4, wherein therelief poppet and the check poppet form a fluid passage from the firstfluid side to the second fluid side when the relief poppet is moved awayfrom the opening in the check poppet.
 6. The valve as set forth in claim1, wherein a spring is positioned between the valve insert stop and aportion of the valve body located in the valve body aperture.
 7. A valvefor use in regulating the flow of fluid between a first fluid side and asecond fluid side in a hydraulic circuit, comprising: a generallycylindrical body comprising an aperture extending from a first end ofthe generally cylindrical body to a second end of the generallycylindrical body; a first valve component extending into the aperturefrom the first end of the generally cylindrical body; a second valvecomponent attached to the first valve component proximate to the secondend of the generally cylindrical body; wherein attachment of the firstvalve component to the second valve component forms a volume with aplurality of openings and prevents the first valve component from beingremoved from the aperture, but permits the first and second valvecomponents to move axially with respect to the generally cylindricalbody; and wherein a relief poppet and a relief spring are located in thevolume, and the relief poppet is biased against one of the plurality ofopenings by the force of the relief spring.
 8. The valve as set forth inclaim 7, wherein the first valve component comprises a check poppet anda valve insert and the second valve component comprises a valve stop. 9.The valve as set forth in claim 7, wherein the first valve componentcomprises a valve insert and a valve stop and the second valve componentcomprises a check poppet.
 10. The valve as set forth in claim 7, furthercomprising a check spring positioned between the first valve componentand the valve body.
 11. The valve as set forth in claim 7, furthercomprising a check spring positioned between the second valve componentand the valve body.
 12. A unitary valve mechanism for use in connectionwith a separate member including a hydraulic circuit having a firstfluid side and a second fluid side, the unitary valve mechanismcomprising: a valve body comprising a first end with a first opening, asecond end with a second opening and an aperture extending from thefirst opening to the second opening, wherein the aperture has a firstdiameter; and a valve insert assembly extending through the aperture andaxially slidable with respect to the valve body, the valve insertassembly comprising a relief poppet, a relief spring, an insert bodyhaving a second diameter and a valve stop at a proximal end of theinsert body, the valve stop engaging a first surface on the valve bodyadjacent the first opening to limit axial movement of the valve insertassembly with respect to the valve body in one direction, and a checkpoppet at a distal end of the insert body, the check poppet engaging asecond surface on the valve body adjacent the second opening to limitaxial movement of the valve insert assembly with respect to the body ina second direction, opposite the first direction, wherein at least oneof the first surface or the second surface on the valve body ispositioned between the valve stop and the check poppet; wherein a fluidflow space is created between the first diameter and the seconddiameter, and wherein fluid passes through the fluid flow space as itflows from the first fluid side to the second fluid side of thehydraulic circuit; and wherein the relief poppet is biased by the reliefspring against an opening formed in the check poppet.
 13. The unitaryvalve mechanism as set forth in claim 12, further comprising a checkspring positioned between the valve body and the valve insert assembly.14. The unitary valve mechanism as set forth in claim 13, wherein theinsert body is selectively engaged to the check poppet.
 15. The unitaryvalve mechanism as set forth in claim 14, wherein the valve stop isintegrally formed on the insert body.
 16. The unitary valve mechanism asset forth in claim 13, wherein the insert body is integrally formed onthe check poppet and selectively engaged to the valve stop.